As many onlookers observe, 16-year-old Derrick Jackson, of Denver, puts his mark on a giant Spalding NBA basketball Thursday at the All-Star Jam Session in the Colorado Convention Center. His message: Look out for your boy. The opening ceremony for the five-day event was held Thursday evening with Denver Mayor John Hickenlooper, NBA commissioner David Stern and Denver Nuggets teammates Earl Boykins and Carmelo Anthony on hand.